1. Field of the Invention
The invention relates to a rotary machine element in which at least one functional part performs movements into nominal stop positions or into mechanical terminal stop positions which are functionally related and whose individual actual position values can be detected independent from one another with at least one position sensor. The invention further relates to a method for detecting position values of at least one functional part of such a rotary machine element.
2. Description of the Related Art
The alignment and clamping of workpieces, in particular, of crankshafts and camshafts, is carried out generally by hydraulically actuated chucks as a rotary machine element. In this connection, the workpiece can be received in a centered or floating arrangement by the chuck. Generally, the chuck comprises, dependent on the workpiece arrangement, several functions which can be carried out during the clamping process usually only in a temporal sequence one after another. Such functions are, for example, centering, clamping, as well as radial, axial, and rotary alignment of the workpiece. These functions are carried out by the corresponding functional parts, such as centering tips, alignment elements, and clamping elements. The functional states are monitored by control functions, for example, recognition of the workpiece type, control whether a workpiece is present or absent, or the like. During the clamping process, mechanical stop positions are conventionally present in the chuck, for example, when the clamping jaws or the centering tip impact on the workpiece. These stop positions are nominal positions which result from the workpiece geometry, for example, the clamping diameter. Further stop positions result when the maximum stroke of the individual chuck functions is reached, dependent on the mechanical chuck configuration, i.e., in the end position of the stroke, respectively. These stop positions are the terminal stop positions.
For controlling the different stop positions the respective mechanical movement of a functional part is coupled conventionally to one or more control rods whose positions are controlled by means of contactless proximity switches in combination with adjusting cams. Since particularly during alignment and clamping of crankshafts and camshafts a plurality of these chuck functions are necessary, numerous such proximity switches are required accordingly. The adjusting expenditure of these terminal proximity switches is high because the switching positions of each individual stop position must be adjusted by the adjusting cams. One proximity switch is thus required for each stop position. They must be adjusted with a relatively high precision. This high adjusting sensitivity, however, can result in faulty messages when vibrations occur, for example, in the case of residual imbalance of a lathe, as a result of machining vibrations on milling machines, or as a result of unavoidable concentricity deviations of the adjusting cams.
A further problem occurs when the stop positions to be controlled are changed as a result of, for example, workpiece dimensions which are not constant or a different type of workpiece. In this situation, the switching positions must be manually corrected or adjusted, which results in a cost-intensive downtime of the machine, maintenance work, repairs, and adjusting work.
A further disadvantage of conventionally employed control devices of a chuck resides in that a safe and reliable course of the functions is carried out serially and therefore is time-intensive with regard to machine cycles. For example, only after checking that the nominal position of a function has been reached, the next function is initiated. With this method it is prevented that, for example, clamping of the workpiece begins already during an accidentally delayed alignment movement. The mechanical position of a chuck function moreover is known to the control device only in those positions where the terminal proximity switches are provided. Intermediate positions between the individual terminal proximity switches are not detected.
Chucks are known tram DE 200 12 080 in which the mechanical position of the piston rod is detected by a control system based on magnetostrictive sensors. The position sensors are used in analogy to terminal proximity switches. i.e., the nominal positions provided during the course of the function or the terminal stop positions are controlled. Additional functions, for example, NC-controlled (NC=numerical control) moving of the chuck functions between the stop positions, measuring, checking, or moving for determining a reference point, are not realized.
Also, a servo device is known (DE 199 54 634) which enables detection of the respective position of the clamping piston by induction. This system is also used only for controlling the nominal positions or the terminal stop positions.
It is an object of the present invention to configure the rotary machine element of the aforementioned kind and the method of the aforementioned kind such that in a constructively simple way the functional part can be monitored with high precision.
In accordance with the present invention, this is achieved in regard to the rotary machine element in that the position sensor is located within a control and/or regulating path between the functional part and an NC-control which path is active in positions between the nominal stop positions and/or the mechanical terminal stop positions.
In accordance with the present invention, this is furthermore achieved in regard to the method in that the actual position values of the functional parts are detected and, based thereon, the speed and acceleration of the functional parts is determined by means of the NC-control.
The rotary machine element according to the invention is characterized in that the position sensor is located in a control and/or regulating path between the functional part and the NC-control. The control and/or regulating path (for short xe2x80x9ccontrol pathxe2x80x9d) is active in positions between the nominal stop positions and/or the mechanical terminal stop positions. The position sensor enables efficient diagnostic methods particularly in the nominal position or in the mechanical terminal stop position. Procedures for a simplified detection or determination of the nominal position, also referred to as reference point methods, are enabled by the position sensor. The control and regulating function is enabled by a continuous and highly precise measurement of the actual position of the functional part.
The determination of the actual position value of the functional part enables with high precision the determination of speed and acceleration. Also, travel distances, speeds, and accelerations for the functional part can be defined. When the rotary machine element has several functional parts, the travel distances, speeds, and accelerations can be defined for each functional part individually.
The movements of the individual functional parts which are functionally correlated with one another are carried out in a precise relation to one another. The travel distances, speeds, and accelerations for each functional part are advantageously programmed, processed, and saved in data processing devices (computer) or in numerical control devices (NC-devices).
By employing the position sensor and by employing corresponding software programs and data processing devices (computers), these functions can be measured, checked, monitored, and controlled, and combinations of these tasks can be carried out. Processing of data and transmission of required information to peripheral devices is carried out advantageously by software.
The measuring of the actual position values by means of the position sensor is advantageously a length measurement. In this case, the respective functional part of the machine element according to the invention performs an axial movement which is detected by the position sensor.
It is also possible that the measurement of the actual position values by means of the position sensor is an angular position measurement. In this case, the angular position of the respective functional part is detected by the position sensor.
Advantageously, the position sensor operates based on the measuring principle of magnetostriction. For this purpose, one or several position sensors as well as one or several position transducers measure (acquire) the actual position values of one or several functional parts. The measurement of angular positions can be realized with this measuring principle by a grooved component which is positioned on the axis of rotation (rotary axis) of the rotary machine element and, when rotated, affects the magnetic field and in this way enables a precise correlation of the angular position relative to the position sensor.
When the rotating machine element is a chuck, it is possible to clamp one or several workpiece types with a different geometry, respectively, in a simple and reliable way. The respective course of movement of the functional parts of the chuck, such as a centering tip, alignment elements, and clamping elements, are processed and saved by NC-programs.
In this connection, the measuring and checking functions can relate to the clamping diameter and workpiece length, optionally also to additional workpiece features.
When the rotary machine element is a workpiece carrier for receiving a workpiece, the measuring function of the workpiece carrier can be used advantageously for an automatic recognition of a workpiece type. This recognition of the workpiece type is used advantageously for automatic recognition of different types of workpieces which reach the production process in a random sequence.
The measuring, checking, monitoring, and control functions are advantageously carried out for an automated recognition of deviations from a predetermined movement course of the clamping process, for example, a workpiece not being present or similar events.
Also, the measuring, checking, monitoring, and control functions can be employed for automatic recognition of impermissible workpiece movements during the machining process, for example, sliding of the workpiece in the chuck as a result of great machining forces. In this case, the position sensor also detects a corresponding sliding movement of the functional part.
When such an impermissible workpiece movement occurs, an adaptive regulation of the chuck functions, machining functions or the like is advantageously carried out, for example, an increase of the clamping force or a reduction of the feeding speed. In this way, an immediate response to such impermissible workpiece movements during the machining process can be carried out so that damage of the workpiece and/or of the tool is reliably prevented.
The measuring function of a clamping chuck can be employed advantageously for a corrective function of parameters within the NC-programs. Such a corrective function can be used, for example, for automatic recognition of the axial or radial length of the workpiece within the chuck or the like.
It is particularly advantageous when the nominal position values have tolerances correlated therewith. When the actual values surpass or drop below these tolerances, the monitoring and control function is activated.
The nominal position values of the function parts required for the respective tool or workpiece are determined by means of a reference movement course by employing a reference workpiece.
It is also possible to preset the nominal position values of the functional parts by programming.
When one or several sensors are exchanged, the rotary machine element is calibrated by performing a reference movement course.
In the same way, the rotary machine element is calibrated by a reference movement course when one or several position transducers are exchanged.